THE NUDIBRANCHES
- Friendly Fins
- Nov 20, 2024
- 4 min read
Updated: Mar 7
Why learn about nudibranchs?
“For us it’s always Carnival! We love to dress up in bright clothes to attract your attention! Most of us are small, but if you look carefully you can easily find us!!!”
How do we recognize nudibranchs?
When we are looking at a snail-shaped mollusk, small and very colorful, we are looking at a nudibranch! Let's see better:
They can be microscopic or reach up to 15 cm in length.
Their name means “naked gills” meaning their gills are visible on the outside of their body or do not exist at all.
“You will surely notice them because they are little tufts that emerge from our backs and float gracefully in the current”
They have two “antennae” called rhinophores which are clearly visible on the dorsal part of their head.
“They are our two “noses”! Thanks to them we can smell in the water!”
Unlike many other mollusks, they have lost their shells.
“We don’t need her to defend us! We’ve developed other super strategies… Read on and find out!”
Where do nudibranchs live?
We can find nudibranchs both in the Mediterranean Sea and in tropical seas, obviously we will encounter different species.
In the Mediterranean:
Nudibranchs prefer rocky and coralligenous seabeds. They love shade and cool water; in fact, it will be easier to find them in winter rather than in summer.
We will often find them in some ravine or cave, even if some like flabellinas love to live on Hydrozoans which they also feed on; therefore, we can see them floating in the current attached to their branches (mostly in winter).
Only some species prefer sandy seabeds.
In tropical seas:
They live everywhere in the coral reefs of the oceans of the world, where they find a large amount of food. The greatest biodiversity of these animals is found in the Indo-Pacific area.
What do nudibranchs eat?
Nudibranchs have specific diets, some feed exclusively on sponges, others on hydrozoans and still others on cnidarians (a large group of animals that includes corals, anemones, etc.).
“To eat this seemingly unappetizing food, we have the radula: a structure equipped with a tiny but powerful hooked dentition that scrapes the surface of our snacks!”
Sometimes it is easier to look for the prey to find the predator! Because they spend the whole day nibbling so:
For example: if we want to see the sea cowfish (which is the most common nudibranch in the Mediterranean Sea) we will look for its favorite prey, a purple sponge called Petrosia Ficiformis; this way we will have a very high chance of finding our friend the cowfish while she is feasting.
“Our diet is closely linked to our defense! We are too smart!
Enemies of nudibranchs
Nudibranchs have no particular enemies precisely because they are absolutely indigestible or toxic! Why?
Let's start from the beginning: cnidarians are organisms equipped with cells called cnidocytes, containing a stinging substance.
Nudibranchs, with a specialized diet of cnidarians, are able to eat these organisms without suffering damage from these cells. In fact... They are able to store them in special appendages of their body called cerata, maintaining their function intact. These cerata are clearly visible on the back and can be used as a defensive weapon if an unwary predator comes forward.
Nudibranchs that feed on sponges are not so unwary: they recover the calcareous spicules present in the sponges and deposit them on the surface of their body, making themselves difficult to digest!
“We might be a little “stuffy”!”
The Life of a Nudibranch
Nudibranchs are simultaneous hermaphrodites: they are both male and female throughout their lives.
During mating, the eggs of both individuals will be fertilized.
The eggs are then laid on the bottom and take on different and spectacular shapes:
Nudibranchs that live in contact with coral reefs and rocky seabeds will lay spiral-shaped eggs, resembling "rosettes" of different colors depending on the species (sometimes we can even trace who makes them! For example, the sea cow makes white rosettes and the Spanish dancer makes red ones)
Nudibranchs that live on hydroids will lay eggs in chains, mostly violet, around the branches of the latter.
Once hatched, the eggs transform into small "larvettes" that will float in the current for a short time until they settle on the bottom and become mini nudibranchs!
Why are nudibranchs so colorful?
Underwater coloration is extremely important for communicating with the rest of the world. Very bright colors are used for various purposes such as courtship, mating and warning. Nudibranchs are very colorful for this purpose.
“Thanks to our splendid colors we warn the would-be predators to stay away from us, because we are not good to eat! In fact we could cause a bad stomach ache!”
But beware of cheaters!!!
Some animals very similar to nudibranchs could take advantage of the resemblance, or still, other animals, during their juvenile and therefore more delicate phase, try to resemble them to have greater protection. This is the case of the juvenile of a species of sea cucumber (Bohadschia graeffi) that does everything to resemble the tropical nudibranch Phyllidia varicosa and ensure protection until it becomes an adult.
"All in all, the brilliant idea is there!"
"Our world is exciting and magical, we convey a great sense of tranquility and our beauty will surely conquer you!"
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